The present invention relates to a lead frame including leads each having a land electrode at an external terminal thereof, to a resin-sealed semiconductor device of land grid array (LGA) type using the lead frame, and to a method for fabricating the same.
With the recent miniaturization of electronic equipment, high-density mounting has been required of semiconductor components including resin-sealed semiconductor devices. To meet the requirement, the semiconductor components have been reduced increasingly in size and thickness. In particular, the resin-sealed semiconductor devices have been increased in the number of pins used therein, while they have been reduced in size and thickness. As a result, a resin-sealed semiconductor device which allows high-density pin placement has been in growing demand.
Referring to the drawings, a lead frame used in a conventional resin-sealed semiconductor device will be described.
FIGS. 9A and 9B show a conventional lead frame of QFP (quad flat package) type, of which FIG. 9A shows a plan structure thereof and FIG. 9B shows a cross-sectional structure thereof along the line IXbxe2x80x94IXb of FIG. 9A.
As shown in FIG. 9A, a lead frame 100 has: a square framework portion 101; a tie-bar portion 102 provided internally of the framework portion 101; suspension leads 103; a die pad portion 104 supported by each of the corners of the die-bar portion 102 and by the suspension leads 103; a plurality of inner leads 105 having respective one ends connected to the tie-bar portion 102 and the respective other ends opposing the die pad portion 104; and outer leads 106 having respective one ends connected to the framework portion 101 and the respective other ends connected to the inner leads 105 via the tie-bar portion 102.
As shown in FIG. 9B, the die pad portion 104 has a chip carrying surface pressed down by a depressing process to be lower in level than the top surfaces of the inner leads 105. The lead frame 100 shown in FIG. 9A is normally arranged in a repeated pattern in the same plane.
FIG. 10 shows a cross-sectional structure of a conventional resin-sealed semiconductor device using the lead frame 100.
As shown in FIG. 10, the conventional resin-sealed semiconductor device has a semiconductor chip 107 fixedly attached onto the die pad portion 104 by using a soldering material or the like. The semiconductor chip 107 is electrically connected to the individual inner leads 105 by metal fine wires 108.
The components disposed internally of the tie-bar portion 102 shown in FIG. 9A, i.e., the semiconductor chip 107, the die pad portion 104, and the inner leads 105 are sealed integrally with a sealing resin material to form a resin-sealed portion 109. The tie-bar portion 102 serves as a resin stopper during the injection of the sealing resin material. After the framework portion 101 is cut away, the tie-bar portion 102 is divided in such a manner as to insulate the outer leads 106 adjacent to each other. The outer leads 106 protruding from each of the side surfaces of the resin sealed portion 109 are processed (by bending) to have respective end portions which are nearly flush with the bottom surface of the resin-sealed portion 109.
In the conventional lead frame 100, however, the width of each of the inner and outer leads 105 and 106 (hereinafter referred to as the leads 105 and 106) is limited if a plurality of semiconductor elements are formed at a higher density in the semiconductor chip 107 and a larger number of pins are used. In such a multi-pin configuration, the number of the leads 105 and 106 is increased accordingly so that the size of the whole lead frame 100 is increased disadvantageously. As a result, the whole resin-sealed semiconductor device is naturally increased in size, which prevents the resin-sealed semiconductor device from being reduced in size and thickness.
If the number of the leads 105 and 106 is increased without changing the outer size of the lead frame 100, the width of each of the leads 105 and 106 should be reduced, which makes it difficult to perform processing such as etching in the fabrication of the lead frame 100.
As a semiconductor device of surface-mount type, there has recently been developed a resin-sealed semiconductor device of, e.g., so-called ball grid array (BGA) type or land grid array (LGA) type wherein a semiconductor chip placed on the top surface of a carrier (wiring board) having external electrodes such as ball electrodes or land electrodes provided on the bottom surface thereof is electrically connected and sealed with a resin. Such a semiconductor device of surface-mount type is mounted on a mother board (mounting board) at the bottom surface thereof and has been becoming mainstream.
Under the circumstances, the problem has been encountered that a semiconductor device of QFP type, i.e., the conventional lead frame 100 in which external electrodes composed of the outer leads 106 are formed only on the side surfaces of the package (resin sealed portion 109) shown in FIG. 10 is incompatible with the grid array type.
On the other hand, the semiconductor device of BGA or LGA type has the problem that production cost cannot easily be reduced since it uses a relatively high-cost carrier (wiring board) as a member for holding a semiconductor chip.
It is therefore an object of the present invention to solve the foregoing conventional problems and thereby provide a lead frame which allows bottom surface mounting by using a frame member integrally formed with a die pad. Another object of the present invention is to increase the reliability of a resin-sealed semiconductor device using the frame member.
To attain the object, a lead frame according to the present invention comprises: a die pad portion supported internally of a framework portion by suspension leads; and a plurality of leads each having one end connected to the framework portion and the other end opposed to the die pad portion, the die pad portion having a holding region formed from a part of an upper surface of the die pad portion which has been elevated above the remaining part thereof, the holding region having an opening formed to extend therethrough in a front-to-back direction of the die pad portion.
If the lead frame according to the present invention is sealed with a resin such that the respective bottom surfaces of the leads are exposed from the bottom surface of a package, the bottom surfaces of the leads form external terminals. This allows an LGA-type package to be implemented by using a frame member without using a wiring board. Since the opening is formed in the holding region for a semiconductor chip to extend therethrough in the front-to-back direction, a sealing resin material is also filled in a space underlying the bottom surface of the die pad portion through the opening so that each of the upper and lower sides of the die pad portion is covered with the sealing resin material. As a result, so-called xe2x80x9cresin balancexe2x80x9d which is the balance between the resin residing in the die pad portion and the resin residing in the semiconductor chip is improved. The improved resin balance prevents the peeling off of the resin or a crack caused in the resin sealed portion by a thermal stress resulting from the difference between the respective thermal expansion coefficients of the die pad portion and the sealing resin material or between those of the semiconductor chip and the sealing resin material and thereby prevents a crack occurring in the semiconductor chip. Accordingly, the reliability of a resin-sealed semiconductor device using the lead frame according to the present invention is increased significantly.
In one aspect of the lead frame according to the present invention, the opening formed in the holding region preferably includes a plurality of openings and one of the openings is provided preferably at a position opposing a position at which an injection gate for a sealing resin material is disposed. In the arrangement, the sealing resin material injected from the injection gate is supplied consistently through the openings positioned in opposing relation to the position at which the injection gate is disposed to the space underlying the holding region. This prevents the occurrence of a void in the resin material filled in the space underlying the holding region.
In another aspect of the lead frame according to the present invention, the opening formed in the holding region preferably includes four openings, the holding region preferably has connecting sections provided between the adjacent openings and a center holding section having a square plan configuration defined by the respective inner edges of the surrounding openings which connect the adjacent connecting sections to each other, and an angle formed between a direction in which the inner edge of at least one of the openings extends and a direction in which the framework portion extends is preferably set to about 45xc2x0.
A resin-sealed semiconductor device according to the present invention comprises: a die pad portion; a semiconductor chip bonded to an upper surface of the die pad portion; a plurality of leads disposed around the die pad portion to be electrically connected to the semiconductor chip by using conductor wires and having respective bottom surfaces exposed; and a resin sealed portion composed of a resin sealing material for integrally sealing the semiconductor chip, the die pad portion, and the plurality of leads, the die pad portion having a holding region formed from a part of an upper surface of the die pad portion which has been elevated above the remaining part thereof, the holding region having an opening formed to extend therethrough in a front-to-back direction of the die pad portion.
Since the resin-sealed semiconductor device according to the present invention is formed by using the lead frame according to the present invention, the sealing resin material is filled also in the space underlying the die pad portion through the opening formed in the holding region of the die pad portion. As a result, each of the upper and lower sides of the die pad portion is covered with the sealing resin material. This prevents the peeling off of the resin, a crack, or the like caused in the resin sealed portion or the semiconductor chip by a thermal stress and thereby increases the reliability of the resin-sealed semiconductor device.
In one aspect of the resin-sealed semiconductor device according to the present invention, the opening formed in the holding region preferably includes a plurality of openings and one of the openings is provided preferably at a position opposing a position at which an injection gate for a sealing resin material used in forming the resin sealed portion is disposed.
In another aspect of the resin-sealed semiconductor device according to the present invention, the opening formed in the holding region preferably includes four openings, the holding region preferably has connecting sections provided between the adjacent openings and a center holding section defined by the respective inner edges of the surrounding openings which connect the adjacent connecting sections to each other and having a square plan configuration, and an angle formed between a direction in which the inner edge of at least one of the openings extends and a direction in which the framework portion extends is preferably set to about 45xc2x0.
In the resin-sealed semiconductor device according to the present invention, the sealing resin material is preferably filled also in a space underlying the holding region of the die pad portion.
In the resin-sealed semiconductor device according to the present invention, that one of the plurality of leads disposed externally of the resin sealed portion preferably has a bottom surface and a side end surface each exposed from the resin sealed portion.
In this case, the plurality of leads are preferably arranged in at least two rows around the die pad portion.
A method for fabricating a resin-sealed semiconductor device according to the present invention comprises: a first step of preparing a lead frame comprising a die pad portion supported internally of a framework portion by suspension leads and a plurality of leads each having one end connected to the framework portion and the other end opposed to the die pad portion: a second step of bonding a semiconductor chip onto the die pad portion; a third step of electrically connecting the semiconductor chip to the plurality of leads by using conductor wires; a fourth step of integrally sealing the semiconductor chip, the die pad portion, and the plurality of leads with a sealing resin material; and a fifth step of separating the resin sealed portion from the framework portion, the die pad portion of the lead frame having a holding region formed from a part of an upper surface of the die pad portion which has been elevated above the remaining part thereof, the holding region having an opening formed to extend therethrough in a front-to-back direction of the die pad portion.
Since the method for fabricating a resin-sealed semiconductor device according to the present invention fabricates a resin-sealed semiconductor device by using the lead frame according to the present invention, the sealing resin material is filled also in the space underlying the bottom surface of the die pad portion through the opening formed in the holding region of the die pad portion in the resin sealing step. As a result, each of the upper and lower sides of the die pad portion is covered with the sealing resin material. This prevents the peeling off of the resin, a crack, or the like caused in the resin sealed portion or the semiconductor chip by a thermal stress and thereby increases the reliability of the resin-sealed semiconductor device.
In one aspect of the method for fabricating a resin-sealed semiconductor device according to the present invention, the opening formed in the holding region preferably includes a plurality of openings and one of the openings is provided preferably at a position opposing a position at which an injection gate for the sealing resin material is disposed.
In another aspect of the method for fabricating a resin-sealed semiconductor device according to the present invention, the opening formed in the holding region of the lead frame preferably includes four openings, the holding region preferably has connecting sections provided between the adjacent openings and a center holding section having a square plan configuration defined by the respective inner edges of the surrounding openings which connect the adjacent connecting sections to each other, and an angle formed between a direction in which the inner edge of at least one of the openings extends and a direction in which the framework portion extends is preferably set to about 45xc2x0.
Preferably, the method for fabricating a resin-sealed semiconductor device according to the present invention further comprises, between the third step and the fourth step, the step of: attaching a sealing sheet material to respective bottom surfaces of the framework portion, the die pad portion, and the plurality of leads such that the sealing sheet material is in close contact therewith.